Fluid ejection devices in inkjet printers provide drop-on-demand ejection of fluid drops. Inkjet printers produce images by ejecting ink drops through a plurality of nozzles onto a print medium, such as a sheet of paper. The nozzles are typically arranged in one or more arrays, such that properly sequenced ejection of ink drops from the nozzles causes characters or other images to be printed on the print medium as the printhead and the print medium move relative to each other. In a specific example, a thermal inkjet printhead ejects drops from a nozzle by passing electrical current through a heating element to generate heat and vaporize a small portion of the fluid within a firing chamber. In another example, a piezoelectric inkjet printhead uses a piezoelectric material actuator to generate pressure pulses that force ink drops out of a nozzle.
When nozzles sit exposed to ambient atmospheric conditions while in idle non-jetting states, evaporative water loss through the nozzle bores can alter the local composition of ink volumes within the bores, the firing chambers, and in some cases, beyond an inlet pinch toward the shelf/trench (ink slot) interface. Following periods of nozzle inactivity, the variation in properties of these localized volumes can modify drop ejection dynamics (e.g., drop trajectories, velocities, shapes and colors). When printing resumes after an inactive, non-jetting period, there is an inherent delay before the local ink volumes within the nozzle bores are refreshed. This delay, and the associated effects on drop ejection dynamics following a non-jetting period, are collectively referred to as decap response. Continued improvement of inkjet printers and other fluid ejection systems relies in part on mitigating decap response issues.